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Appendix IV.

961

Capacities vary considerably, from 30 up to 600 amperes per
cell, according to the number of plates and their size.

Current efficienc/:

discharge ampere hours
charge ampere hours

= 80% to 90%

.~           „ .            discharge Watt hours      f  .. L

Energy efficiency « —=—~^-~7—~---------= 60% to 70%

^             J        charge Watt hours                   '

Both these depend on rates of discharge, the lower figure for
a rapid, and the higher for a slow rate.

Over-discharging, or too strong an acid, may either of them
cause sufyhating of the plate, the second fault being remedied by
the addition of a small quantity of carbonate of soda. Buckling
of the plate is caused by variable action, excessive rates, or by
sulphating ; and disintegration results both from sulphating and
buckling.

For electric lighting, the

VT      £    „      E M F of lamps

No. of cells = —~-------------— -I- 2 or 3

Tor traction, accumulators rapidly deteriorate through vibration
or excessive rates (see next jtaragrapK).

P. 554. Electric Traction.—There are four methods now
in vogue for carrying the current from main to car motors ;

1.  Overhead line, with small trolley.

2.  Conduit, with slot rail.

3.  Surface contact, with temporarily live studs,

4.  Accumulators on the cars.

The overhead or trolley system is by far the cheapest, and,
being very little objectionable, is now most used. The main is
buried in. the ground, and the live wires, one for the up and one
for the down line, are carried on suitable posts and brackets,
being connected to the main through the hollows in the posts. The
current is taken to the motor from the overhead trolley through, a
(fishing rod' (/. 554), and the return is by way of the rail, whose
several parts are connected by ' bonds' at the fish-plates.

The conduit system is so very expensive that it has only been
adopted where appearance has had to be considered. The